Map display apparatus

ABSTRACT

A map display apparatus includes a map data memory which stores map data necessary for plotting a map of a predetermined region; a map display which reads map data out of the map data memory and plots a bird&#39;s-eye view display by projecting the map data read out from the map data memory onto a projection plane which makes a projection angle with a plane of the map data read out from the map data memory, the projection angle being greater than 0° and less than 90°, the bird&#39;s-eye view display including identifying marks which identify items in the bird&#39;s-eye view display; and an identifying mark overlap preventer which prevents identifying marks from overlapping one another in the bird&#39;s-eye view display.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.09/932,951, filed Aug. 21, 2001, now U.S. Pat. No. 6,603,407, which is acontinuation of application Ser. No. 09/320,556 filed on May 27, 1999,now U.S. Pat. No. 6,278,383, which is a divisional of application Ser.No. 08/636,767 filed on Apr. 19, 1996, now U.S. Pat. No. 5,917,436, thecontents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

This invention relates to a map display apparatus for use in anavigation system for measuring the position of a mobile body andreporting the present position to a user, and more specifically to abird's-eye view map display apparatus which provides a map in a morecomprehensible way to the user.

A navigation apparatus mounted to a mobile body processes informationfrom a variety of sensors to measure the position of the mobile body andreports the position to a user. This navigation apparatus comprisesposition measurement means for measuring the absolute position of amobile body, memory means for storing map data constituted bytwo-dimensional vector data obtained by projecting points on the groundsuch as roads and buildings on a plane divided into meshes by universaltransverse Mercator projection and character data accompanying thetwo-dimensional vector data, input means for receiving commands from theuser, and display means for reading the necessary vector data from themap mesh stored in the memory means in accordance with the commandinputted from the input means and conversion processing the data todisplay the map on a display. Here, data conversion processing includesmovement conversion for changing the display position of the map,reduced scale conversion, such as enlargement and reduction, used fordisplaying the map in an arbitrary reduced scale and rotation conversionfor changing the displaying direction of the map. By means of theseprocessings, a plan view map depicting the ground surface directlyoverhead by normal projection is displayed on the display.

In navigation apparatuses, according to the prior art, plan view mapdisplay which depicts a map by normal projection directly overhead hasbeen employed to display the map. When two points spaced apart from eachother are simultaneously displayed, therefore, a reduced scale becomesunavoidably great and detailed information cannot be displayed. One ofthe means for solving this problem is a bird's-eye view display systemwhich displays a map when points having a certain height from the groundsurface are looked down obliquely from afar on a plane. In order toapply this bird's-eye view display to the navigation apparatuses, thefollowing problems must be solved.

First, in the case of the bird's-eye view display which displays abroader range of regions than the plan view map, a reduced scale becomesgreat at points far from the start point, so that a greater quantity ofinformation is displayed. According to the prior art systems, characterstrings of those regions in which the reduced scale becomes great arenot displayed or the character strings in the proximity of a viewpointare merely displayed at the upper part. For this reason, fall-off ofcharacters and overlap of character strings are unavoidable, andrecognizability of the characters by the user drops.

Secondly, background data and character data are constituted in the mapdatabase so that display quality attains the highest level when the planview map is displayed. Therefore, in the bird's-eye view map displaydisplaying a broader range of regions, the frequency of the occurrencethat the same character strings are displayed at a plurality ofpositions becomes higher. Since no counter-measure has been taken in thepast for the same character string, the same character string isunnecessarily displayed and this unnecessary character string hides theroads and other background data. In consequence, display quality getsdeteriorated.

Thirdly, though a route to the destination is displayed in superpositionwith the map in a different color from those of the background roads,all the route data are displayed with the same line width in the pastbecause the concept of the road width does not exist in the vector dataexpressing the routes. However, because the map is expressedthree-dimensionally in the bird's-eye view display, the feel ofthree-dimensional depth will be lost if all the routes are displayed bythe same line width.

In the fourth place, in the display of a driving orbit, it has beencustomary in the prior art to store the position information of drivingin a certain distance interval and to display the points representingthe driving orbit on the basis of the position information so stored.When the driving orbit is displayed by the method of the prior artsystem on the bird's-eye view map, however, the gap of the point stringsrepresenting the orbit is enlarged in the proximity of the viewpoint atwhich the reduced scale becomes small, and the user cannot easilyrecognize which route he has taken. The gap of the dot strings becomesunnecessarily narrow, on the contrary, at portions away from theviewpoint at which the reduced scale becomes great, and the roads andthe character strings as the background information are hidden.Therefore, the user cannot easily recognize the map information, either.

In the fifth place, pattern information, e.g. solid lines and dashlines, used for displaying the vector information such as roads,railways, administrative districts, etc., and pattern information, e.g.check and checkered patterns, used for displaying polygons representingwater systems, green zones, etc., are registered to the map data base.When the map containing these pattern information is displayed bybird's-eye view, the prior art systems execute not only perspectiveconversion of each apex coordinates constituting the lines and thepolygons but also perspective conversion of the patterns for displayingthe map. Therefore, the processing time becomes enormously long, and thetime required for bird's-eye map display gets elongated.

In the sixth place, in order to prevent dispersion of the map datadisplayed near an infinite remote point called a “vanishing point” inthe bird's-eye map display, the display region is limited to theforeground region by a predetermined distance from the vanishing pointand artificial background information such as a virtual horizon and skyare displayed at the depth in the prior art system. However, theseartificial background information in the prior art systems have fixedpatterns or fixed colors and do not match the surrounding conditions.

In the seventh place, when the bird's-eye view map display and the planview map display are switched, the user cannot easily discriminate whichof them is actually displayed when the number of objects plotted issmall. Moreover, the user can operate and change the position of theviewpoint in the bird's-eye view map display, and the map regionactually displayed greatly changes depending on the position of theviewpoint and on the direction of the visual field. In the prior artsystems, however, there is no means for providing the information of theposition of the viewpoint, etc., even when the position of the viewpointand the direction of the visual field are changed, and the systems arenot easy to handle.

In the eighth place, when the bird's-eye view map is displayed, the mapdisplaying direction is set in such a manner that the image displaydirection coincides with the driving direction, as described, forexample, in JP-A-2-244188. When the destination is set, the drivingdirection and the direction of the destination are not alwayscoincident, so that the destination disappears from the screen.Accordingly, there remains the problem that the user cannot recognizethe map while always confirming the direction of the destination.

In the conventional bird's-eye view map display, in the ninth place,even when a map information density is low in a certain specificdirection or when a specific direction comprises only information havingspecific attributes, the display position of the viewpoint, that is, thedisplay position of the present position, does not change on the screen.In other words, there occurs the case where a large quantity ofinformation, which are not much significant, are displayed on thedisplay region having a limited area, and the information cannot beprovided efficiently.

SUMMARY OF THE INVENTION

To solve the first problem, the present invention uses means for judgingwhether or not overlap occurs between character strings or symbols, andselecting and displaying character strings or symbols havingpredetermined attributes when overlap exists, or selecting anddisplaying character strings or symbols in the proximity of theviewpoint, or replacing the overlapping character strings or symbols bya font size smaller than the recommended font size. The characteroverlap judgment means uses means for judging that the character stringsoverlap by using rectangular region information circumscribed with thecharacter strings when the mutual circumscribed rectangular regionsoverlap, or judges that the character strings overlap by usingrectangular region information of rectangles positioned more inside by apredetermined distance from the rectangles circumscribed with thecharacter strings when mutual rectangle regions overlap.

To solve the second problem, the present invention uses means forjudging whether or not the same character strings or symbols existinside the screen displaying a certain bird's-eye view map, andselecting and displaying character strings in the proximity of theviewpoint when the same character string or symbol exists. It iseffective to display both the character strings or symbols if the mutualdistance is great even when the same character strings or symbols exist.Accordingly, the present invention uses means for selecting anddisplaying character strings in the proximity of the viewpoint when thedistance between the same character strings or symbols or the distancebetween them in the bird's-eye view map display is judged as existingwithin a predetermined range, and for displaying both of the characterstrings or the symbols when the distance is judged as existing outsidethe range.

To solve the third problem, the present invention uses means fordisplaying routes in the proximity of the viewpoint by thicker linesthan routes apart from the viewpoint when the routes are displayed onthe bird's-eye view map. Alternatively, the present invention uses meansfor dividing the bird's-eye view map into a plurality of regions anddisplaying routes by a line width inherent to each region when theroutes to be displayed in superposition in these regions are displayed.

To solve the fourth problem, the present invention uses means forobtaining an orbit which supplements the stored orbit information forthe driving routes in the proximity of the viewpoint, and displaying theorbit in superposition with the bird's-eye view map. As to drivingorbits away from the viewpoint, on the other hand, the present inventionuses means for thinning out the stored orbit information and displayingthe orbits so thinned out in superposition on the bird's-eye view map.

To solve the fifth problem, the present invention uses means forexecuting perspective conversion the lines constituting the map data andeach apex coordinates constituting polygons, and displaying the polygonsor the lines by using the patterns used for plan view map display byusing the coordinates values after perspective conversion.

To solve the sixth problem, the present invention uses means forlimiting display of the map in the foreground regions by a predetermineddistance from the vanishing point and changing the colors or patterns ofthe artificial background such as the horizon and the sky to bedisplayed at the depth. More concretely, the present invention usesmeans for changing the colors or the patterns of the artificialbackground information by a blue color representing the sky when lampsare not lit and by a black or grey color when the lamps are lit, byusing signals representing the condition of the car, that is, light turnON/OFF signal of the car.

To solve the seventh problem, the present invention uses means forcausing a map display control portion to switch the bird's-eye view mapand the plan view map in accordance with a user's request, and causing amenu display portion, which displays a mark in superposition with themap, to receive the change of the display state of the map and todisplay the mark representing the plan view map in superposition withthe map when the map is switched from the bird's-eye view map to theplan view map. When the map is switched from the plan view map to thebird's-eye view map, the mark representing the bird's-eye view map isdisplayed in superposition with the map. When the user changes theposition of the viewpoint during the display of the bird's-eye view map,the shape of the mark representing the present position is changed andis displayed in superposition with the map.

To solve the eighth problem, the present invention promotes the user toset the destination. After setting of the destination is completed, thedirection of the viewpoint is brought into conformity with the directionof the destination from the position of the viewpoint, and theposition/direction of the viewpoint and the projection angle arecalculated so that the map of predetermined regions is displayed by thebird's-eye view map. Even when the present position is updated, theprocessing described above is always executed repeatedly to bring theposition of the viewpoint into conformity with the present position andto display the bird's-eye view map.

To solve the ninth problem, a region inside the bird's-eye view map,which has a low map information density, and a region constituted byinformation having only specific attributes are retrieved. When theseregions are retrieved, the position of the viewpoint is changed so thatthe region having a low map information density and the regioncomprising only the information of the specific attributes do not occupya large area on the display screen. The bird's-eye view map is displayedby using the information of the position of the viewpoint and theprojection angle so obtained.

When overlap exists between the character strings in the bird's-eye viewmap display, the first means displays one of them, or displays theoverlapping character strings by changing their size to the smallerfonts.

When the same character strings or symbols exist in the bird's-eye viewmap display, the second means selects and displays the character stringscloser to the viewpoint.

In the bird's-eye view map display, the third means so functions as todisplay the guiding route near the viewpoint by a greater line widththan the guide routes existing away from the viewpoint.

In the bird's-eye view map display, the fourth means so functions as todisplay the dot strings representing the driving orbit with suitablegaps between the region near the viewpoint and the region far from theviewpoint.

In the bird's-eye view map display, the fifth means so functions as tospeed up the display of pattern lines and polygons in which patternsexist.

In the bird's-eye view map display, the sixth means so functions as todisplay the artificial background in different colors or differentpatterns in accordance with the condition of the car.

In the bird's-eye view map display, when the bird's-eye view map and theplan view map are mutually switched, the seventh means so functions asto change the shape of the mark to be displayed in superposition withthe map in the direction of the position of the viewpoint and the visualfield.

In the bird's-eye view map display, the ninth means so functions as toreduce the occupying area of the regions having a low map informationdensity or comprising only information of specific attributes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, shows a bird's-eye view map display according to an embodimentof the present invention;

FIG. 2 is an explanatory view showing a perspective conversionprocessing of a map;

FIGS. 3A, 3B, 3C and 3D are explanatory views showing a perspectiveconversion process of a map;

FIG. 4 is a structural view of a navigation apparatus according to anembodiment of the present invention;

FIG. 5 is a hardware structural view of an arithmetic processing portionof the embodiment of the present invention;

FIG. 6 is an explanatory view showing appearance of a navigationapparatus according to an embodiment of the present invention;

FIG. 7 is a functional structural view of an arithmetic processingportion for accomplishing bird's-eye view map display;

FIG. 8 is a flowchart of map plotting means for accomplishing bird's-eyeview map display;

FIG. 9 is a flowchart of coordinates conversion means for accomplishingbird's-eye view map display;

FIG. 10 is a flowchart of perspective conversion computation foraccomplishing bird's-eye view map display;

FIG. 11 is a flowchart of display position computation for accomplishingbird's-eye view map display;

FIG. 12 is a flowchart of plotting judgment means for accomplishingbird's-eye view map display;

FIGS. 13A and 13B are flowcharts of polygonal and linear patterndisplays in bird's-eye view map display;

FIG. 14 is a flowchart of character string display in bird's-eye viewmap display;

FIG. 15 is a flowchart of character plotting means;

FIGS. 16A, 16B, 16C and 16D show an embodiment for character fringingdisplay for representing one character by a plurality of characters;

FIGS. 17A and 17B show an embodiment for character clipping processing;

FIGS. 18A to 18J show an embodiment for display means of a fringedcharacter;

FIG. 19 is a flowchart of a route display in bird's-eye view mapdisplay;

FIG. 20 is a flowchart of orbit display in bird's-eye view map display;

FIG. 21 is a flowchart of artificial background display in bird's-eyeview map display;

FIG. 22 is a flowchart of mark display in plan view map display andbird's-eye view map display;

FIGS. 23A, 23B and 23C are explanatory views useful for explaining asetting method of a viewpoint and a projection plane in bird's-eye viewmap display;

FIGS. 24A, 24B, and 24C are explanatory views useful for explaining asetting method of a viewpoint and a projection plane in bird's-eye viewmap display;

FIGS. 25A and 25B show an embodiment for optimization display of thepresent position in bird's-eye view, map display;

FIGS. 26A, 26B, 27A, 27B, 28A, 28B, 29A and 29B show an embodiment forcharacter string overlap judgment in bird's-eye view map display;

FIGS. 30A, 30B, 31A, 31B, 32A, 32B; 33A and 33B show an embodiment forcharacter string overlap judgment in bird's-eye view map display;

FIGS. 34A, 34B, 35A, 35B, 36A, 36B, 37A and 37B show an embodiment forcharacter string overlap judgment in bird's-eye view map display;

FIGS. 38A, 38B and 38C show an embodiment for avoiding character stringoverlap display in bird's-eye view map display;

FIGS. 39A and 39B show an embodiment for avoiding character stringoverlap display in bird's-eye view map display;

FIGS. 40A, 40B,and 40C show an embodiment for displaying the samecharacter string in bird's-eye view map display;

FIGS. 41A, 41B, and 41C show an embodiment for polygonal and linearpattern display in bird's-eye view map display;

FIGS. 42A and 42B show an embodiment for route display in bird's-eyeview map display;

FIGS. 43A and 43B show an embodiment for orbit display in bird's-eyeview map display;

FIGS. 44A and 44B show an embodiment for artificial background displayin bird's-eye view map display;

FIGS. 45A and 45B show an embodiment for mark display in plan view mapdisplay and bird's-eye view map display; and

FIGS. 46A and 46B show an embodiment for present position mark displayin bird's-eye view map display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an example of the bird's-eye view map displayed by abird's-eye view map display device mounted to a navigation systemaccording to an embodiment of the invention. The bird's-eye view mapdisplay device according to this embodiment generates a bird's-eye view102 showing a bird's-eye view from a specific position as a projectionchart of two-dimensional map data (indicated by reference numeral 101 inFIG. 1), and displays it on a display screen of a display 2.Incidentally, in the bird's-eye view 102 shown in FIG. 1, a folded line103 is provided with a thick line and is highlighted in order torepresent a guiding route. An artificial background 104 represents thesky, a mark 105 represents the present position and an orbit mark 106represents the orbit of a car so far driven. Further, arrows in FIG. 1represent the relationship of projection from the two-dimensional mapdata 101 to the bird's-eye view 102.

The outline of bird's-eye view map display as the characterizing featureof the present invention will be explained with reference to FIG. 2.

In printed map charts or in the navigation systems according to theprior art, a map is represented by a plan map display obtained when agiven area is viewed from an infinitely remote point above this area.Because this plan map display has the advantage that a reduced scale isconstant irrespective of points inside the same display screen, the feelof distance is easy to grasp. When an area between certain two points isrepresented on the same screen, however, the operation for adjusting andoptimizing the reduced scale of the map display becomes necessary, andif the distance between these two points is great, only limitedinformation can be displayed because the quantity of information thatcan be displayed at one time is restricted by the size of the displayused and the level of its precision. Bird's-eye view display is employedas means for solving this problem. When this bird's-eye view display isused, the information of those portions which are close to the viewpointis enlarged while the information of those remote from the viewpoint isreduced, as is obvious from FIG. 2. Therefore, when the area betweencertain two points is displayed on the same screen, the point for whichmore detailed information is required is situated close to the viewpointwith the other being remote from the viewpoint, and their mutualpositional relationship is represented in an easily comprehensible formby displaying the two points on the same screen. Further, a greaterquantity of information can be provided to the user on the informationnear the viewpoint. This bird's-eye view display can be accomplished byeffecting perspective conversion which projects two or three-dimensionalmap information of a plane A to a plane B describing a certain angle θwith the plane A. Since two-dimensional map data can be used as the mapinformation used, bird's-eye view display is feasible by adding theperspective conversion function to existing navigation systems withoutadding new map data, but various contrivances must be made when thebird's-eye view display is put into practical use.

FIG. 4 shows a structural example of a navigation apparatus for a mobilebody to which the present invention is applied.

Hereinafter, each structural unit of this navigation apparatus will beexplained. A processor unit 1 detects the present position on the basisof the information outputted from various sensors 6 to 9, reads the mapinformation necessary for display from a map memory unit 3 on the basisof the present position information so detected, graphically expands themap data, displays this data on a display 2 by superposing a presentposition mark, selects an optimum route connecting the destinationindicated by the user to the present position and guides the user byusing a speech input/output device 4 or the display 2. In other words,it is a central unit for executing various processings. The display 2 isthe unit which displays the graphic information generated by theprocessor unit 1, and comprises a CRT (Cathode-Ray Tube) or a liquidcrystal display. A signal S1 between the processor unit 1 and thedisplay 2 is generally constituted by RGB signals or NTSC (NationalTelevision System Committee) signals. The map memory device 3 comprisesa large capacity memory medium such as a CD-ROM or an IC card andexecutes read/write processing of the required map data. S2 is a signalbetween the processor unit 1 and the map memory device 3. The speechinput/output device 4 converts the message to the user generated by theprocessor unit 1 to the speech signals, outputs them, recognizes theuser's voice and transfers it to the processor unit 1. S3 is a signalbetween the processor unit 1 and the speech input/output device 4. Aninput device 5 is the unit that accepts the user's instruction, andcomprises hard switches such as scroll keys 41, reduced scale keys 42and angle changing keys 43 shown in FIG. 6, for example, a joystick,touch panels bonded on the display 2, or the like. S4 is a signalbetween the processor unit 1 and the input device 5. The sensors usedfor detecting the position in the navigation system for a mobile bodycomprise a wheel speed sensor 6 for measuring the distance from theproduct of the circumference of a wheel and the number of revolutions ofthe wheel and measuring a turning angle of the mobile body from thedifference of the numbers of revolutions of the wheels forming a pair, aterrestrial magnetic sensor 7 for detecting the magnetic field of theearth and detecting the moving direction of the mobile body, a gyrosensor 8 for detecting the turning angle of the mobile body such as anoptical fiber gyro or an oscillation gyro, and a GPS receiver 9 forreceiving signals from a GPS satellite, measuring the distance betweenthe mobile body and the GPS satellite and the change ratio of thisdistance for at least three satellites and thus measuring the presentposition of the mobile body, its traveling direction and its course. Theinput device further includes a traffic information receiver 10 forreceiving signals from beacon transmitters and FM multiplex broadcastingthat transmit weather information and traffic information such as roadjamming information, closed-to-traffic information, parking lotinformation, etc., and outputting received information S9 to theprocessor unit 1. Furthermore, an internal LAN device 11 is provided soas to receive various information of the car such as door open/closeinformation, the information on the kind and condition of lamps turnedON, the information of the engine condition, the information on theresult of trouble-shooting, and so forth, and output car information S10to the processor unit 1.

FIG. 5 is an explanatory view showing the hardware construction of theprocessor unit.

Hereinafter, each constituent element will be explained. The processorunit 1 employs the construction wherein devices are connected by a bus.The devices include a CPU 21 for executing computation of numericalvalues and controlling each device, a RAM 22 for storing the map and theoperation data, a ROM 23 for storing the program and the data, a DMA(Direct Memory Access) 24 for executing data transfer at a high speedbetween the memory and the memory and between the memory and eachdevice, a plotting controller 25 for executing at a high speed graphicplotting such as expansion of vector data to pixel information, etc.,and for executing display control, a VRAM 26 for storing graphic imagedata, a color palette 27 for converting the image data to the RGBsignals, an A/D converter 28 for converting analog signals to digitalsignals, an SCI 29 for converting serial signals to parallel signals insynchronism with the bus, a PIO 30 for establishing synchronism with theparallel signal and putting it on the bus, and a counter 31 forintegrating pulse signals.

FIG. 7 is a explanatory view useful for explaining the functionalconstruction of the processor unit 1.

Hereinafter, each constituent element will be explained. Presentposition calculation means 66 integrates on the time axis the distancedata and the angle data obtained by integrating the distance pulse dataS5 measured by the wheel speed sensor 6 and the angular velocity data S7measured by the gyro 8, respectively, and calculates the position (X′,Y′) after driving of the mobile body from the initial position (X, Y).In order to bring the rotating angle of the mobile body into conformitywith the azimuth of driving, the azimuth data S6 obtained from theterrestrial magnetic sensor 7 and the angle data obtained by integratingthe angular velocity data from the gyro 8 are mapped on the 1:1 basis,and the absolute azimuth of the driving direction of the mobile body iscorrected. When the data obtained from the sensors described above areintegrated on the time axis, the sensor errors accumulate. Therefore, aprocessing for canceling the errors so accumulated is executed in acertain time interval on the basis of the position data S8 obtained fromthe GPS receiver 9, and the present position information is outputted.Since the present position information acquired in this way contains thesensor errors, map-match processing means 67 executes map-matchprocessing so as to further improve positional accuracy. This is theprocessing which collates the road data contained in the map in theproximity of the present position read by the data read processing means68 with the driving orbit obtained from the present position calculationmeans 66, and brings the present position to the road having the highestsimilarity of shape. When this map-match processing is executed, thepresent position coincides in most cases with the driving road, and thepresent position information can be accurately outputted. The presentposition information calculated in this way is stored in orbit memorymeans 69 whenever the mobile body drives a predetermined distance. Theorbit data is used for plotting an orbit mark on the road on thecorresponding map for the road through which the mobile body has run sofar.

On the other hand, user operation analysis means 61 accepts the requestfrom the user by the input device 5, analyzes the content of the requestand controls each unit so that a processing corresponding to the requestcan be executed. When the user requests to guide the route to thedestination, for example, it requires the map plotting means 65 toexecute processing for displaying the map for setting the destinationand further requests route calculation means 62 to execute processingfor calculating the route from the present position to the destination.The route calculation means 62 retrieves a node connecting between twodesignated points from the map data by a Dijkstra algorithm, etc., andstores the route so obtained in route memory means 63. At this time, itis possible to determine the route in which the distance between the twopoints is the shortest, the route through which the destination can bereached within the shortest time or the route through which the drivingcost is the lowest. Route guiding means 64 compares the link informationof the guide route stored in the route memory means 63 with the presentposition information obtained by the present position calculation means66 and the map match processing means 67 and notifies to the userwhether or not to drive straight or whether or not to turn right or leftbefore passing by a crossing, etc., by the speech input/output device 4,displays the traveling direction on the map displayed on the display,and teaches the route to the user. Data read processing means 68 sooperates as to prepare for reading the map data of the requested regionfrom the map memory device 3. Map plotting means 65 receives the mapdata around the point for which display is requested from the data readprocessing means 68 and transfers the command for plotting thedesignated object in the reduced scale, the plotting direction and theplotting system that are designated, respectively, to graphic plottingmeans 71. On the other hand, menu plotting means 70 receives a commandoutputted from the user operation analysis means 61 and transfers acommand for plotting various kinds of requested menus and marks to bedisplayed in overlap with the map to graphic processing means 71. Thegraphic processing means 71 receives the plotting commands generated bythe map plotting means 65 and the menu plotting means 70, and expandsthe image on the VRAM 26.

FIG. 8 is an explanatory view useful for explaining the functions of themap plotting means 65.

Hereinafter, each constituent element will be explained. Display regionjudgment means 81 decides the display reduced scale of the map anddecides also which region should be displayed with which point of themap data as the center. Initial data clip means 82 selects, by clipprocessing, the data necessary for display from the line data, the plandata and the character data representing objects such as roads,buildings, etc., necessary for subsequent processings from each mesh ofthe map data read out by the data read processing means 68 from the mapmemory device 3, the line data comprising recommended routes and storedin the route memory means 63 and the point data comprising drivingorbits and stored in the orbit memory means 69, on the basis of theinformation set by the display region judgment means 81. The clipprocessing algorithms hereby used include a Cohen-Sutherland line clipalgorithm for the line and point data and a Sutherland-Hodgman polygonclip algorithm for the plan and character data (Foley et al., ComputerGraphics, pp. 111-127, Addison-Wesley Publishing Company). Thisprocessing can reduce the data quantity which should be subsequentlysubjected to coordinates conversion and plotting processing and canimprove a processing speed.

Coordinates conversion means 83 enlarges or reduces the map dataobtained by the clip processing to the target size and when an objectmust be displayed by rotating it, this means 83 so functions as toeffect affine conversion of each coordinates value of the map data.Plotting judgment means 84 so functions as to select those data whichare practically necessary for plotting by using the map data obtained bythe coordinates conversion means 83. When the reduced scale is great,for example, the data quantity to be plotted substantially increases.Therefore, this means 84 so functions as to omit small roads and thenames of places which may be omitted, and to eliminate character stringsthat are displayed in superposition with one another. Data clip means 85so functions as to select the map data relating to the plotting areafrom the map data obtained from the plotting judgment means 84, by clipprocessing. The clip processing algorithm hereby used may be the samealgorithm used by the initial data clip means. Further, this processingmay be omitted. Artificial background setting means 86 provides thefunction which is necessary for bird's-eye view map display and displaysthe artificial background such as the horizon, the sky, etc., in orderto reduce the plotting data quantity and to improve the screenrecognition property. Plotting command generation means 87 generatescommands for plotting lines, polygons, characters, etc., so as to plotthe resulting point, line and plane data as well as the character databy the designated colors and patterns, and the command for setting thecolors and the patterns and outputs them to the graphic processing means71.

Next, the fundamental display system of the bird's-eye view map displaywill be explained with reference to FIGS. 3A, 3B, 3C, 3D and FIG. 8.

At first, the region for bird's-eye view display is decided by thedisplay region judgment means 81 from the position of the viewpoint andthe direction of the visual field and from the angle θ (projectionangle) described between the plane A and the plane B in FIG. 2 (step 1in FIG. 3A). When a bird's-eye view is displayed on a rectangulardisplay, map data of a narrow region is necessary for the area near theviewpoint and map data of a broad region is necessary for the arearemote from the viewpoint. Therefore, the map data of a trapezoidal meshregion in the drawings is plotted finally. Next, the necessary map datais extracted by the initial data clip means 82 from the map mesh datainclusive of the region for bird's-eye view display by using therectangular regions which are circumscribed with the trapezoidal regionto be practically plotted (step 2 in FIG. 3B). Next, the coordinatesconversion means 83 enlarges or reduces the extracted data and thenexecutes affine conversion so that the trapezoid stands upright.Further, perspective conversion is executed so as to convert eachcoordinates value of the map data to the data which is representedthree-dimensionally (step 3 in FIG. 3C). In this instance, perspectiveconversion is expressed by the following equations (1) and (2) where theposition coordinates of the viewpoint are (Tx, Ty, Tz), the anglebetween the plane A and the plane B is θ, the map data coordinatesvalues before conversion are (x, y) and the map data coordinates valuesafter conversion are (x′, y′): $\begin{matrix}{x^{\prime} = \frac{T_{x} + x}{T_{z} + {{y\quad \cdot \sin}\quad \theta}}} & (1)\end{matrix}$

$\begin{matrix}{y^{\prime} = \frac{T_{y} + {{y \cdot \cos}\quad \theta}}{T_{z} + {{y\quad \cdot \sin}\quad \theta}}} & (2)\end{matrix}$

The trapezoid represented at the step 2 in FIG. 3B is subjected tocoordinates conversion into the rectangular region represented at thestep 3 in FIG. 3C whereas the rectangle circumscribed with the trapezoidrepresented at the step 2 in FIG. 3B is subjected to coordinatesconversion into a deformed rectangle circumscribed with the rectanglerepresented at the step 3 in FIG. 3C, by perspective conversion,respectively. Because the portions other than the rectangular regionneed not be plotted, these portions other than the rectangular regionare clipped by the data clip means 85 (step 4 in FIG. 3D). The plottingcommand generation means 87 generates the plotting command by using themap data so obtained, and the graphic processing means 71 conductsplotting to the VRAM 26 so that the bird's-eye view map shown in FIG. 1can be displayed.

Next, the perspective conversion parameters in bird's-eye view mapdisplay, that is, the angle 0 between the map and the projection plane(projection angle) and the coordinates (Tx, Ty, Tz) of the origin of theviewpoint coordinates system containing the projection plane, which isviewed from the object coordinates system containing in turn the mapplane, or in other words, the method of calculating the position of theprojection plane, will be explained with reference to FIGS. 23A, 23B and23C. It is desired for the navigation apparatus to display in detail thepoint at which the user is now driving, that is, the region around thepresent position. Therefore, the explanation will be given on the casewhere the present position is displayed at the lower center portion ofthe screen as shown in FIG. 23C. To accomplish bird's-eye view display,it is judged whether rotation of map is necessary at step 1002, and inthe event the rotation is considered necessary then the angle φ betweenthe driving direction vector and the base of the map mesh is firstdetermined at the step 1004 in FIG. 9, and affine conversion forrotating the map data to be plotted by the angle φ is executed for eachdata constituting the map (step 1005). Since bird's-eye view display isjudged as being made at the step 1006, the flow proceeds to theprocessing for calculating the projection angle θ and the position ofthe viewpoint (steps 1008 and 1009). The projection angle θ is set to anangle near 0° when it is desired to make display so that the differenceof the reduced scale becomes small between the portions near theviewpoint and the portions away from the viewpoint, and is set to near900 when it is desired to make display so that the difference of thereduced scale becomes great between the portions near the viewpoint andthe portions away from the viewpoint. Normally, the projection angle θis set to the range of about 30° to about 45°. Since the user desires toarbitrarily set the map region to be displayed by bird's-eye view mapdisplay, the projection angle θ can be set by the projection anglechange key 43 provided to the navigation apparatus shown in FIG. 6. Whenthis key 43 is so operated as to increase the projection angle θ, theprojection angle θ increases, so that the map of remote regions isdisplayed. When the key 43 is so operated as to decrease the projectionangle θ, the projection angle θ decreases, so that the map near thepresent position is displayed.

Next, as to the position (Tx, Ty, Tz) of the projection plane,calculation is executed at the step 1009 so that the difference (Ax, Ay,Az) obtained by subtracting the position (Tx, Ty, Tz) of the position ofthe projection plane from the present position (x, y, z) is always aconstant value. As the absolute values, further, Δx is set to 0, Δz isset to a small value when display is made by a small reduced scale inmatch with the reduced scale of the map display and to a large reducedscale when display is made by a large reduced scale. Normally, Δz isdecided preferably so that the reduced scale of the plane view iscoincident with the reduced scale of a certain point near the center ofbird's-eye view display. Since the reduced scale of the map ispreferably changeable in accordance with the user's request, the step1009 operates in such a manner as to set Δz to a small value when theuser designates a small reduced scale by the reduced scale key 42provided to the navigation apparatus shown in FIG. 6 and to a largevalue when a large reduced scale is designated. The Δy value may beeither a positive value or a negative value but this embodiment uses thenegative value and sets it so that the present position is displayed ata lower ⅓ position of the screen. Step 1010 executes perspectiveconversion of each coordinates value of the map data by using theprojection angle θ and the position (Tx, Ty, Tz) of the projection planethat are obtained in the manner described above.

The detail of this perspective conversion operation will be explainedwith reference to FIG. 10. First, whether or not the plane dataconstituted by polygons such as water systems, green zones, etc., existis judged (step 1020). When the result proves YES, perspectiveconversion is executed for each node constituting the polygon (step1021). This operation is executed for all the polygons (step 1022).Next, when the line data constituting the map such as the roads, therailways, the administrative districts, etc., and the optimum route fromthe present position to the destination are calculated, whether or notthe line data representing the route exist is judged (step 1023). Whenthe result proves YES, perspective conversion is executed for each nodethat constitutes the line (step 1024). Further, when the character dataconstituting the map such as the area names, symbols, etc., and theorbit are displayed, whether or not the point data representing theorbit exist is judged (step 1026). As to the character strings such asthe area names, symbols, etc., it is advisable to handle one pointrepresenting a given character string such as the upper left end pointof the character string as the point data. When these point data arejudged as existing, perspective conversion is executed for each nodeconstituting the point (step 1027) and is then executed for all thepoints (step 1028). The graphic processing means 71 executes plottingprocessing by using the map data so obtained. In consequence, inbird's-eye view map display shown in FIG. 23C, the driving direction isalways displayed in the UP direction on the screen and the presentposition is always displayed at the same point on the screen.

Next, the explanation will be given on the display method of thebird's-eye view map, which can be easily recognized by the driver, whena certain destination is designated by the input device 5 from the mapor the retrieved screen, will be explained with reference to FIG. 9 andFIGS. 24A, 24B and 24C. It is desired for the navigation apparatus todisplay in detail the point at which the user is driving at present,that is, the area near the present position. Therefore, the presentposition is displayed at the center lower portion of the screen, moreconcretely at the lower ⅓ region of the transverse center of the screen,as shown in FIG. 24C. To accomplish bird's-eye view display shown inFIG. 24C, the angle o between the line perpendicular to the lineconnecting the present position to the destination shown in FIG. 24A andthe base of the map mesh is first determined at the step 1004 in FIG. 9and affine conversion is executed by the angle φ for each coordinatesvalue of the map data to be plotted (step 1005). Since this bird's-eyeview display is judged as being made at the step 1006, the flow thenproceeds to the processings for calculating the projection angle θ andthe position of the viewpoint (steps 1008 and 1009). The projectionangle θ is set to an angle near 0° when it is desired to make display sothat the difference of the reduced scale between small between theportions near the viewpoint and the portions away from the viewpoint,and is set to an angle near 90° when it is desired to make display sothat the difference of the reduced scale becomes great between theportions near the viewpoint and the portions away from the viewpoint.Normally, the projection angle θ is set to the range of about 30° toabout 45°. Since the user desires to arbitrarily set the map region tobe displayed by bird's-eye view map display, the projection angle θ canbe set by the projection angle change key 43 provided to the navigationapparatus shown in FIG. 6. When this key 43 is so operated as toincrease the projection angle θ, the projection angle e increases, sothat the map of remote portions is displayed. When the key 43 is sooperated as to decrease the projection angle θ, the projection angle θdecreases, so that the map near the present position is displayed.

Next, as to the position (Tx, Ty, Tz) of the projection plane,calculation is made at the step 1009 so that the difference (Δx, Δy, Δz)obtained by subtracting the position (Tx, Ty, Tz) of the projectionplane from the present position (x, y, z) becomes always a constantvalue. As the absolute values, Δx is set to 0, and Δz is set to a smallvalue when display is made by a small reduced scale in match with thereduced scale of the map displayed, and to a great value when display ismade by a large reduced scale. Normally, Δz is preferably set so thatthe reduced scale of the plan view is coincident with the reduced scaleof a certain point near the center of bird's-eye view display. Since theuser desires to change the reduced scale of the map, the step 1009 sooperates as to set a small value to Δz when the user designates a smallreduced scale by the reduced scale key 42 provided to the navigationapparatus shown in FIG. 6 and to set a large value to Δz when the userdesignates a large reduced scale. The Δy value may be either a positivevalue or a negative value, but this embodiment uses the negative valueand determines the value so that the present position can be displayedat the lower ⅓ position of the screen. The step 1010 executesperspective conversion of each coordinates value of the map data byusing the projection angle θ and the position (Tx, Ty, Tz) of theprojection plane so obtained, and the graphic processing means 71executes the plotting processing by using the resulting map data.Consequently, in bird's-eye view display shown in FIG. 24C, thedestination is always displayed in the UP direction and the presentposition is always displayed at the same position on the screen. Thenavigation apparatus becomes easier to operate by switching theoperation mode to the mode in which the destination and the presentposition are fixed always at certain two points on the screen when thecar moves to the position where the destination can be displayed on thescreen.

Incidentally, the polygon representing the Imperial Palace, the greenzones and the water systems such as sea and lakes are not much useful asthe information for the driver driving the car having the navigationapparatus, as shown in FIG. 25A. Rather, a greater quantity ofinformation which is directly necessary for driving, such as the roadinformation, are displayed preferably on the limited screen. Means forsolving this problem will be explained with reference to FIG. 11. Theinformation of the roads and the background are represented by thenodes, and the node density of the polygons representing the green zonesand the water systems such as sea and lakes tends to be lower than thenode density of the lines such as the roads. Therefore, the greatestquantity of information of the roads, etc., are displayed by optimizingthe display region in the transverse direction of the screen, for theregion displayed in the longitudinal direction, in accordance with theinitial value. This processing is executed by the display positioncalculation routine at the step 1011 in FIG. 9. First, whether the modeis for executing optimization of the display position is judged (step1040). When optimization is judged as to be executed, the nodes that arepractically displayed on the screen are extracted from the nodesconstituting the lines and the polygons subjected to perspectiveconversion at the step 1041 by clip calculation (step 1041). Further,the difference Δx between the x coordinates arithmetic mean value x1obtained at the step 1042 and the x-coordinates value x2 at the centerof the screen is calculated (step 1043). At the next step 1044, thedifference Δx obtained by the step 1043 is added to the x-coordinatesvalue of the nodes constituting the line and the polygon. The graphicprocessing means 71 executes the plotting processing by using the mapdata obtained in this manner. In consequence, bird's-eye view mapdisplay capable of displaying a greater quantity of those informationwhich are directly necessary for driving, such as the roads, can bedisplayed on the screen as shown in FIG. 25B.

Next, the method of the plotting processing of the objects constitutingthe bird's-eye view map will be explained more concretely. The plottingjudgment means 84 shown in FIG. 12 operates in such a manner as tooptimally display the plan data, the line data and the character dataconstituting the map, the route data calculated in accordance with therequest from the user and the orbit data representing the route so fardriven, respectively.

First, whether or not the plane data exists in the plotting data isjudged (step 1060). When the plane data is judged as existing, the flowproceeds to the plane data plotting processing (step 1061) shown in FIG.13A. The plane data plotting processing judges whether the plane patternexists inside the polygon to be practically plotted or whether the fullplane should be smeared away (step 1080). When the plane pattern is notjudged as existing, pattern setting is so effected as to smear away theentire portion inside the polygon and the processing is completed (step1081). When the plane pattern is judged as existing, whether or notperspective conversion is to be executed for the plane pattern is judged(step 1082). When the plane pattern is subjected to perspectiveconversion and is displayed, the pattern has the feel of depth asdepicted in FIG. 41A and can be therefore displayed morethree-dimensionally. However, the plotting time gets elongated becausethe processing quantity becomes greater. When the plane pattern used forplan view map display is displayed, on the other hand, the displaybecomes planar as depicted in FIG. 41B, but the processing can be madeat a higher speed because the plane pattern can be handledtwo-dimensionally. Therefore, when a higher processing speed isrequired, perspective conversion of the pattern is judged as unnecessaryat the step 1082 and the designated pattern itself is set as the patterndata (step 1083). When display quality has higher priority, on the otherhand, perspective conversion of the pattern is judged as necessary atthe step 1082. Therefore, the pattern is subjected to perspectiveconversion and the conversion result is set as the pattern data (step1084). The method shown in FIG. 41C may be employed as means forimproving this processing speed. This method divides a polygon into aplurality of regions (four regions shown in the drawing) in thedirection of depth and smearing away each region by using the meanpattern obtained by subjecting the plane pattern to perspectiveconversion in each of the region. Since the pattern becomes atwo-dimensional pattern inside the region according to this method, theprocessing speed can be improved.

Next, whether or not the line data exists in the plotting data is judged(step 1062). When the line data is judged as existing, the processingshifts to the line data plotting processing (step 1063) in FIG. 13B. Inthis line data plotting processing, whether the line pattern exists inthe lines practically plotted or is smeared by solid lines is judged(step 1085). When the line pattern is not judged as existing, patternsetting is effected so as to draw the solid lines and the processing iscompleted (step 1087). When the line pattern is judged as existing,whether or not perspective conversion is to be effected for the linepattern is judged as step 1087). When the line pattern is subjected toperspective conversion and is displayed, the feel of depth develops asshown in FIG. 41A and representation can be made morethree-dimensionally. However, the plotting time gets elongated in thiscase because the processing quantity increases. When display is made bythe line pattern used for plan view map display, display becomes planaras shown in FIG. 41B, but high speed processing can be made because theline pattern can be handled one-dimensionally. Therefore, when a higherprocessing speed is required, perspective conversion of the pattern isnot judged as necessary at the step 1087 and the designated patternitself is set as the pattern data (step 1088). On the other hand, whenhigher priority is put to display quality, perspective conversion of thepattern is judged as necessary at the step 1087. Therefore, the patternis subjected to perspective conversion and the converted result is setas the pattern data (step 1089).

Next, whether or not the character data exists in the plotting data isjudged (step 1064). When the character data is judged as existing, theprocessing proceeds to the character data plotting processing (step1065) in FIG. 14. The character data plotting processing judges whichattribute each character string in the map has, the attribute being oneof a plurality of attributes such as names of places, names ofbuildings, map symbols, etc. (step 1100), selects character stringshaving predetermined attributes that must be displayed essentially, andhands over the processing to the step 1101. Since the character stringhaving the attributes that must be essentially displayed is selected,buffering is made so as to display this character string at the step1101. Next, overlap of one character string with another is judged (step1102). There are a plurality of methods for judging overlap of thecharacter strings.

The first method will be explained with reference to FIGS. 26A, 26B,27A, 27B, 28A, 28B, 29A and 29B. This method calculates the polygonencompassing the character string (the outer frame of the polygon shownin FIGS. 26A and 26B) and judges the overlap of the characters by usingthe polygonal region information (the hatched pattern region of thepolygon shown in FIGS. 27A and 27B) constituted by a region positionedinward by a predetermined number of bits from the polygon. According tothis method, the character strings are judged as overlapping when theoverlap judgment regions (the hatched pattern regions of the polygons)overlap with one another as shown in FIGS. 28A and 28B. When thecharacter overlap judgment regions do not overlap as shown in FIGS. 29Aand 29B, the character strings are not judged as overlapping. Generally,the respective character strings can be discriminated even when thecharacters overlap to some extent, and this system operates in such amanner that overlap of the character strings to some extent are notjudged as overlapping. Accordingly, the overlapping character stringsare not omitted more than necessary, and the quantity of information tobe transmitted to the driver increases.

Next, the second method will be explained with reference to FIGS. 30A,30B, 31A, 31B, 32A, 32B, 33A and 33B. This method calculates therectangular regions circumscribed with the character string (therectangles shown in FIGS. 30A and 30B) and judges overlap of thecharacter strings by using the rectangular region information (thehatched rectangular regions shown in FIGS. 31A and 31B). According tothis method, when the overlap judgment regions of the character strings(the hatched rectangular regions) overlap with one another as shown inFIGS. 32A and 32B, the character strings are judged as overlapping. Whenthe character overlap judgment regions do not overlap with one anotheras shown in FIGS. 33A and 33B, the character strings are not judged asoverlapping. Since this method can judge overlap of a plurality ofcharacter strings by a simple shape of the rectangle, the minimum andmaximum values of the rectangle in the x- and y-axis directions may bemerely compared between the overlapping character strings, and theoperation time can be therefore shortened.

Finally, the third method will be explained with reference to FIGS. 34A,34B, 35A, 35B, 36A, 36B, 37A and 37B. This method calculates therectangular region circumscribed with the character string (therectangle of the outer frame shown in FIGS. 34A and 34B) and judgesoverlap of the character strings by using the rectangular regioninformation (the hatched rectangular pattern region shown in FIGS. 35Aand 35B) constituted by a region positioned inward by a predeterminednumber of dots from the rectangle. According to this method, thecharacter strings are judged as overlapping when the overlap judgmentregions of the character strings (the hatched rectangular patternregions) overlap with one another as shown in FIGS. 36A and 36B. Thecharacter strings are not judged as overlapping when the overlapjudgment regions do not overlap with one another as shown in FIGS. 37Aand 37B. Generally, the respective character strings can bediscriminated even when overlap of characters occurs to some extent, andthis system operates in such a manner that the character strings are notjudged as overlapping even when they overlap to some extent. Therefore,the overlapping character strings are not omitted more than necessary,and the quantity of the information to be transmitted to the driverincreases. Further, because overlap of a plurality of character stringsis judged by a simple shape of the rectangle, the minimum and maximumvalues in the x- and y-axis directions may be merely compared between aplurality of character strings, and the operation time can be shortened.

When overlap of the character strings is judged as existing afteroverlap is judged by any of the three kinds of character overlapjudgment means described above, the attributes of the overlappingcharacter strings are examined (step 1103). When the attributes of theoverlapping character strings are judged as different, the characterstrings having the attributes which are decided as having higherpriority for display are selected and are buffered (step 1104). Such anembodiment is shown in FIGS. 38A, 38B and 38C. It will be hereby assumedthat the initial state has the screen structure such as shown in FIG.38A, and comprises the symbol attributes constituted by symbols such asdouble circles and the post marks, and the character string attributesconstituted by the character strings. If the symbol attributes are to bepreferentially displayed when the processing of the step 1104 isexecuted, the symbol attributes are preferentially displayed when thecharacter string and the symbol overlap with each other as shown in FIG.38B. In other words, the position at which “double circle” and the placename “Marunouchi” overlap with each other is displayed by the “doublecircle” and at the position at which the postal symbol “” overlaps withthe place name “Kandabashi” is displayed by the symbol “”. Next, whenthe attributes of the character strings are judged as the same as aresult of examination of the attributes of the overlapping characterstrings (step 1103), sorting is then effected in the depth-wisedirection for the character string (step 1105). Further, the characterstring close to the present position is selected and is then buffered(step 1106). Such an embodiment is shown in FIG. 38C. Here, if thecharacter strings overlap with each other when the processing of thestep 1106 is executed, the character string closer to the presentposition is displayed. In other words, when the name “Tokyo” and thename “Marunouchi 2” overlap, “Tokyo” is displayed, and when the name“Hitotsubashi” and “Ohtemachi” overlap, “Ohtemachi” is displayed. Theexplanation given above deals with the method of selecting anddisplaying the character strings when the character strings overlap, butthere is still another method which replaces display of the overlappingcharacter strings by small fonts and displays them as shown in FIGS. 39Aand 39B. In other words, when overlap of the character strings is judgedas existing at the step 1102 in FIG. 14, these character strings aredisplayed in the font size smaller than the designated font size. If thedesignated font size of characters is 24×24 pixels, for example, displayis made in the font size of 16×16 pixels or 12×12 pixels. Since overlapof the character strings becomes smaller as shown in FIG. 39B in thiscase, recognition performance of the character strings can be improved.Next, whether or not the same character string, which expresses the samecharacters in the same sequence, exists in the character strings isjudged (step 1107). When the same character string is judged asexisting, the distance between the character strings is then calculated(step 1108). Here, the term “distance between the character strings”represents the difference of the position data of the characters put onthe map data or the difference of the position data of the characterswhen the character strings are displayed on the bird's-eye view map. Tocalculate the distance, it is advisable to use one point representingthe character string, that is, the upper left end point or the centralpoint of the character string. Whether or not the distance between thecharacter strings so calculated falls within a predetermined area isjudged (step 1109) and when the result proves YES, the character stringsin the proximity of the present position are buffered (step 1110). Theoperation example will be explained with reference to FIGS. 40A, 40B and40C. Under the initial state shown in FIG. 40A, four character stringsrepresenting an interchange exist. The distances between these characterstrings are calculated as shown in FIG. 40B, and the character stringsin the proximity of the present position, which has small distances, areselected, while both character strings are selected for those havinglarge distances. In consequence, the character strings are displayed asshown in FIG. 40C. As can be clearly understood from these drawings, thecharacter strings which are not necessary as the information are omittedand only the character strings which are absolutely necessary are left.Therefore, the driver can more easily recognize them.

Next, the character plotting means 1185, which can be inserted as asubroutine to the final step of the flowchart shown in FIG. 14, will beexplained concretely with reference to FIG. 15.

Here, whether or not decorated characters, or the like, are designatedas a character style is first judged (step 1201). The decoratedcharacters include bold-faced characters having a thick character lineso as to highlight the characters and fringed characters having abackground color or a frame of a designated specific color around thelines constituting a given character in order to have the character morecomprehensible when it is displayed in superposition in a region where alarge number of lines and planes are displayed as the background.Reference numeral 2181 in FIG. 18A represents an example of such afringed character. This fringed character can be plotted in thefollowing way. First, character plotting is effected for a character tobe fringed at a position of one dot 2182 (FIG. 18B) from the upper leftof the coordinates in which the object character is to be plotted, inthe background color. Further, character plotting is effected eighttimes, in total, in the same way by using the background color at anupward position by one dot 2183 (FIG. 18C), at a right upward positionby one dot 2184 (FIG. 18D), at a left position by one dot 2185 (FIG.18E), at a right position by one dot 2186 (FIG. 18F), at a left downwardposition by one dot 2187 (FIG. 18G), at a downward position by one dot2188 (FIG. 18H) and at a right downward position by one dot 2189 (FIG.181), respectively. Finally, the intended character is plotted at thedesignated coordinates position in the designated color (2191 in FIG.18J). As a modified example of the fringed characters, there is a methodwhich displays the background color in the predetermined directions ofthe character, for example, to the right, down and right downward, or aframe having a designated specific color.

When the character is not judged as the decorated character in thecharacter style judgment, the relation between the designated characterand the clip region is judged by clip judgment (step 1207) so as to callthe character plotting routine having, or not having, the clip in thepixel unit. The clip processing routine compares the character plottingstart coordinates, for example, the left lower end point of thedesignated character, with the clip region and judges whether or not theleft lower end point of this character is contained in the clip region2162, the plotting region 2161 or other regions, as shown in FIGS. 17Aand 17B. By the way, when the character to be plotted is the standardcharacter, the clip region is expanded to the left by the width of thecharacter and in the down direction by the height of the character fromthe plotting region. Assuming that the height of the standard characterand the half-size character is h, the width of the standard character isw, the width of the half-size character is w′, the left lower end pointof the plotting region is (x1, y1) and the right upper end point is (x2,y2), for example, the left lower end point of the clip region in thestandard character is (x1-w′, y1-h), its right upper end point is (x2,y2), the left lower end point of the clip region in the half-sizecharacter is (x1-w′, y1-h) and its right upper end point is (x2, y2).The left lower end points of the characters indicated by referencenumerals 2163 and 2167 in FIGS. 17A and 17B exist outside the clipregion. Therefore, the characters are clipped by clipping and nothing isplotted. The left lower end points indicated by reference numerals 2164and 2168 in FIGS. 17A and 17B exist inside the clip region but are notcontained in the plotting region. Therefore, the routine for executingthe clip processing on the pixel unit is called, and character plottingis reliably executed, though the processing speed is not high (step1209). The left lower end points of the characters indicated byreference numerals 2165 and 2169 in FIGS. 17A and 17B are contained inthe plotting region. Therefore, the clip processing is omitted in thepixel unit, and character plotting is executed at a high processingspeed (step 1208). Since the processing is executed in this way, highspeed character plotting can be accomplished. Incidentally, thecharacter plotting start coordinates are hereby set to the left lowerend point of the character, but when the character plotting startcoordinates are set to the position offset by a predetermined value fromthis left lower end point of the character, the offset distance may beadded to the coordinates values of the plotting region and the clipregion.

When the character is judged as having decoration in the character stylejudgment 1201, whether or not the designated character constitutes onecharacter by a plurality of characters is judged (step 1202). As anexample of one character string constituted by a plurality of characters2142, there is a character 2141 of the shape having a size which exceedsthe size that can be expressed by one character 2142 as shown in FIG.16A. When decoration is applied in a character unit to such a characterstring, a fringe 2143 is displayed at the boundary of a respectivecharacter 2142 in the case of a fringed character, for example, as shownin FIG. 16B, and display quality drops. Therefore, when a plurality ofcharacters are judged as constituting one character string, the flowjumps to the routine which does not put decoration to the characters.Incidentally, there is a method which examines the character codes andjudges that a plurality of characters constitute one character stringwhen the codes are within a predetermined region, as a method of judgingthat a plurality of characters constitute one character string.Accordingly, in the case of the decorated characters such as the fringedcharacters, too, the fringe 2143 is not displayed at the boundary ofeach character 2142 and display quality can be improved. The operationsafter the clip judgment 1207 are the same as in the foregoingexplanation.

Next, when a plurality of characters are not judged as constituting onecharacter string at the step 1202, whether or not the designatedcharacter is displayed in superposition with other characters is judged(step 1203). Here, whether or not the designated character overlaps witha plurality of characters that constitute one character is evaluated.The decorated characters such as the fringe characters intend to displaymore comprehensively those characters which overlap with the backgroundinformation such as the lines and planes. When the decorated charactersuch as the fringed character is displayed when overlapping charactersexist as shown in FIG. 16C, the overlapped character string becomesdifficult to discriminate. There is also the case where one symbol, orthe like, is displayed by combining the character constituting onecharacter by a plurality of characters with characters to be displayedin superposition with the former, and in such an application, thecharacters to be displayed in superposition need not be the decoratedcharacters. Therefore, whether or not the designated character isdisplayed in superposition with other characters is examined at the step1203, and when it is, the flow jumps to the routine which does not putdecoration to the character. In consequence, display such as shown inFIG. 16D is executed, and intended display can be accomplished. Theoperations after the clip judgment 1207 is the same as in the foregoingembodiment.

Next, when the designated character is not judged as being displayed insuperposition with other characters at the step 1203, plotting of thedecorated characters is executed. The relation between the designatedcharacter and the clip region is judged by the clip judgment (step 1204)and the character plotting routine having, or not having, the clip inthe pixel unit is called. The clip processing routine compares theplotting start coordinates of the character such as the left lower endpoint of the designated character with the clip region, and judgeswhether or not the left lower end point of the character is contained inthe clip region 2162, the plotting region 2161 or other regions in FIGS.17A and 17B. When, for example, the height of the character is h, thewidth of the character is w, the left lower end point of the plottingregion is (x1, y1) and the right upper end point is (x2, y2), the lowerend point of the clip region is (x1-w, y1-h) and the right upper endpoint is (x2, y2). When the left lower end point of the character existsoutside the clip region, it is excluded by clipping and nothing isplotted. When the left lower end point of the character exists insidethe clip region and is not contained in the plotting region, plotting ofthe decorated character is reliably executed by the clip processing inthe pixel unit, though the processing speed is not high (step 1206).When the left lower end point of the character is contained in theplotting region, the clip processing in the pixel unit is omitted, andplotting of the decorated character is executed at a high processingspeed (step 1205). When such a processing is executed, characterplotting can be accomplished at a high speed. In this explanation, theplotting start coordinates of the character are set to the left lowerend point of the character, but when the plotting start coordinates ofthe character are set to a point offset by a certain predetermined valuefrom this left lower end point of the character, this offset may beadded to the coordinates value of the boundary between the plottingregion and the clip region.

Next, whether or not the route data exists in the plotting data isjudged (step 1066). When the route data is judged as existing in theroute memory means, the processing shifts to the route data plottingprocessing (step 1067). The route data plotting processing 1067 dividesthe region in which the map is practically displayed into a plurality ofzones in the depth-wise direction, and applies necessary processing ineach region. The explanation will be given hereby on the case where theregion is divided into four zones. First, whether or not the route dataexists in the foremost front side region 1 inclusive of the presentposition is judged (step 1120) and when the result proves YES, the linewidth for displaying the route is set to the greatest width (e.g. 9-dotwidth; step 1121). Next, whether or not the route data exists in theregion 2 above the region 1 is judged (step 1122) and when the resultproves YES, the line width representing the route is set to the widthsmaller than that of the step 1121 but greater than that of the step1125 (e.g. 7-dot width: step 1123). Next, whether or not the route dataexists in the region 3 above the region 2 is judged (step 1124), andwhen the result proves YES, the line width representing the route is setto the width smaller than that of the step 1123 but greater than that ofthe step 1127 (e.g. 5-dot width; step 1125). Finally, whether or not theroute data exists in the deepest region 4 is judged (step 1126) and whenthe result proves YES, the line width representing the route is set to awidth smaller than that of the step 1125 (e.g. 3-dot width; step 1127).When plotting is carried out in this manner, the forehand route can bedisplayed thinly and the depth route, thickly, as shown in FIG. 42Bunlike the prior art system which does not have the feel ofthree-dimensional depth shown in FIG. 42A. Accordingly, the driver canrecognize very naturally the route data. Incidentally, the explanationis hereby given on the system which divides the region and changes theline width for each divided region. However, it is also possible toemploy the method which displays the routes close to the presentposition by a thicker line and the routes away from the present positionby a thinner line.

Next, whether or not the orbit data exists in the plotting data isjudged (step 1068). When the orbit data is judged as existing, theprocessing shifts to the orbit data plotting processing (step 1069)shown in FIG. 20. Incidentally, this orbit data is stored in the orbitmemory means 69 storing therein the driving position in a predetermineddistance interval. Generally, when the orbit data is displayed on themap by bird's-eye view map display, the gap of the points representingthe orbit near the present position becomes great, whereas time gap ofthe points representing the orbit becomes small at the positions awayfrom the present position. Therefore, there occurs the case from time totime where the points of the orbit overlap with one another. To solvethis problem, in the orbit data plotting processing (step 1069), orbitthinning-out region judgment means (step 1140) for judging whether theregion for which the orbit is to be plotted is away from the presentposition, switches the processing to the step 1141 if the orbit is theorbit of the position away from the present position. Thinning-out dataquantity calculation means (step 1141) decides the thinning-out quantityof the orbit data displayed so that the gap of the points representingthe orbit becomes easily comprehensible when bird's-eye view map displayis executed (step 1141). The orbit thinning-out processing (step 1142)thins out the orbit data, which need not be displayed, from the data tobe displayed in accordance with the thinning-out quantity of the orbitdata determined by the step 1141, and prevents the orbit data from beingdisplayed for the positions away from the present position. Next, theorbit interpolation region judgment means (step 1143) for judging if theregion for which the orbit is to be plotted is near the presentposition, judges whether or not the orbit to be displayed is near thepresent position, and when the orbit is judged as being near the presentposition, the processing shifts to the step 1144. The interpolation dataquantity calculation means (step 1144) decides the orbit data quantityto be interpolated afresh between the orbit and the orbit so that thegap of the points representing the orbit reaches the comprehensible dataquantity when bird's-eye view map display is executed (step 1144). Theorbit interpolation processing sets the orbit data to be afreshdisplayed between the orbit and the orbit and on the driving road inaccordance with the interpolation quantity of the orbit data decided bythe step 1144, prevents the interval between the orbit data frombecoming too great and displays comprehensibly the roads that have beentaken in the proximity of the present position (step 1145).

Next, the orbit display examples are shown in FIGS. 43A and 43B. In theprior art system, the orbit data represented by the circles ◯ isdisplayed in such a manner as to broaden at portions in the proximity ofthe present position and to narrow at portions away from the presentposition as shown in FIG. 43A. In the present system, on the other hand,the orbit data is displayed with equal gaps at the portions in theproximity of the present position and at the portion away from it asshown in FIG. 43B. Accordingly, display quality can be improved and theroads containing the orbits can be more easily recognized. Therefore,the orbit recognition factor by the driver can be improved.

The explanation given above explains the plotting processing method ofthe objects constituting the bird's-eye view map. Next, the method ofplotting the artificial background such as the sky and the horizon willbe explained. One of the problems encountered in bird's-eye view map isthat when the map of the far places from the present position isdisplayed as shown in FIG. 44A, its reduced scale becomes small, anextremely enormous quantity of map data are necessary in plotting, anelongated time is necessary for display and high speed response cannotbe obtained. To solve this problem, the inventors of the presentinvention have proposed the method which limits the far region from thepresent position to be displayed in the map so as to reduce the map dataquantity and displays instead artificial objects such as a horizon, asky, and so forth. More concretely, the display region judgment means 81shown in FIG. 8 decides the region to be displayed practically on themap. After the bird's-eye view map is displayed through the subsequentmeans 82 to 85, the artificial background setting means 86 sets the dataof the artificial background. The content of this processing will beexplained with reference to FIG. 21. First, an artificial backgroundregion calculation means (step 1161) reads out the region informationwhose map is decided to be displayed by the display region judgmentmeans 81, and decides the region for which the artificial background isdisplayed, from the difference between this region information and thescreen size information. Next, artificial background color setting means(step 1162) and artificial background pattern setting means (step 1163)decide the colors of the background region and its pattern on the basisof various information such as the car information and the timeinformation. The method of deciding the colors on the basis of the carinformation will be hereby explained by way of example. The carinformation S10 is inputted to the processor portion through the car LAN11. When a side marker lamp of the car is lit at this time, it meansthat the surroundings are dark and the time can be judged as night.Therefore, the artificial background is displayed in black or grey. Whenthe side marker lamp is not lit, the time can be judged as daytime.Therefore, the artificial background is displayed in blue. When the bluecolor cannot be displayed due to the color palette, it is advisable toconduct dither processing which sets the pattern so that the blue colorand the white color are sequentially displayed.

Next, another embodiment which obtains the similar effect by a differentmeans will be explained. In the navigation apparatus, the date and thetime can be acquired by receiving and analyzing the signals from the GPSsatellite. The artificial background can be displayed by using thisinformation so that the blue color is displayed when the time is judgedas daytime and the black or grey color is displayed when the time isjudged as night. The artificial background may be displayed in redrepresenting the morning or evening glow for the morning or the evening.Next, still another embodiment for obtaining the similar effect by adifferent means will be explained. This is the system which displays theartificial background in blue when the weather is fine and in grey whenthe weather is rainy or cloudy, by using the weather informationcontained in the information S9 received by the traffic informationreceiver 10. Since the artificial background is displayed to match withthe surrounding conditions by these means, the driver can easily judgewhat is represented by the artificial background.

Next, display means for the additional information such as the means tobe displayed in superposition with the bird's-eye view map will beexplained. The navigation apparatus for displaying the bird's-eye viewmap improves the user, interface by displaying the informationrepresenting by which system the map presently displayed is plotted, insuperposition with the map. Menu plotting means 70 for executing thisprocessing will be explained with reference to FIG. 22. The content ofthe user's operation is transmitted by the input device 5 to the useroperation analysis means 61, where the content is analyzed. When thenecessity of display by the menu plotting means 70 is judged asexisting, the content is transmitted to the menu plotting means 70 byusing a message. Receiving this message, the menu plotting means startsits processing and judges whether or not the request of this message isthe display request of the plan view map (step 1180). When the messageis judged as the one requesting the display of the plan view map, a markrepresenting that the plan view map such as shown at the lower left ofFIG. 45A is now being displayed is displayed (step 1181). Further, themark representing the reduced scale of the map displayed at present isdisplayed (at the lower right of FIG. 45A; step 1182). When the messageis not the one described above, whether or not the request of themessage is the display request of the bird's-eye view map is judged(step 1183). When it is judged as the message requesting display of thebird's-eye view map, the mark representing that the bird's-eye view mapis now being displayed, such as the one shown at the lower left of FIG.45B, is displayed (step 1184). Further, the mark representing thereduced scale of the map presently displayed is turned off (step 1185).When the message is not the one described above (step 1186), whether ornot the request of the message is the change request of the projectionangle θ in the bird's-eye view map is judged (step 1186). When it isjudged as the message requesting the change of the projection angle θ,the shape of the mark representing the present position shown in FIG.45B is changed in accordance with the projection angle θ as shown inFIGS. 46A and 46B (step 1187). When the projection angle θ is close to0, that is, when the bird's-eye view map is close to the plan view map,the shape of the present position mark is brought into conformity withthe shape of the present position mark in the plan view map display, andas the projection angle θ approaches 90°, the shape of the presentposition mark is subjected to perspective conversion in accordance withthe projection angle θ and a present position mark having the convertedshape is used for display. As a result of the processing describedabove, the driver can easily judge the display mode of the map and thedisplay region, so that recognition performance can be improved.

The foregoing embodiments can reduce overlap of the character strings inthe bird's-eye view map display, eliminate the necessary for the user toestimate what is the character string displayed, from the relationbetween the preceding and subsequent character strings, and can make thecharacter strings and the symbols more easily comprehensible. Becausethe bird's-eye view map is easily recognizable even while the driver isdriving, safety can be further improved.

Since display of the same character string is eliminated in thebird's-eye view map display, the bird's-eye view map can be displayedmore simply. In consequence, the bird's-eye view map can be recognizedmore easily even while the driver is driving, and safety can be furtherimproved.

Because the route near the viewpoint is displayed more thickly than theroutes away from the viewpoint in the bird's-eye view map display, themap can be expressed more three-dimensionally. Therefore, the user caneasily acquire the feel of depth of the bird's-eye view map, and a morecomprehensible map can be obtained.

Further, because the dot strings representing the driving orbit in thebird's-eye view map display are expressed with suitable gaps at bothportions away from the viewpoint and portions near the viewpoint, thephenomenon in which the gaps of the dot strings representing the orbitbecomes great, that occurs in the proximity of the viewpoint, as well asthe phenomenon in which the gaps of the dot strings representing theorbit becomes narrower than necessary, that occurs at portions away fromthe viewpoint, can be avoided, and display quality of the bird's-eyeview map and the driving orbit can be improved.

Display quality of the patterns contained in the lines and the planes inthe bird's-eye view map display somewhat drops, but because the displaytime can be shortened, the time necessary for displaying the bird's-eyeview map becomes shorter. Therefore, the redisplay cycle of thebird's-eye view map becomes shorter, and the bird's-eye view map can bedisplayed more really.

The artificial background representing the virtual sky and horizon areso displayed as to correspond to the surrounding condition in thebird's-eye view map display. Therefore, the user is not perplexedunnecessarily.

Further, the user can easily judge that the map presently displayed isthe bird's-eye view map or the plan view map. Since the presentcondition is displayed in such a manner as to correspond to the changeof the viewpoint, the navigation apparatus becomes easier to use andsafety can be improved.

Since the destination is always displayed in a predetermined direction,the driver can drive the car while confirming always the direction ofthe destination.

Since the information desired by the driver is preferentially displayed,the necessity for the driver to conduct unnecessary operations decreasesduring driving, safety can be therefore improved further.

What is claimed is:
 1. A navigation apparatus comprising: a road mapdata reader for obtaining road map data; an angle setter for setting alook down angle so as to generate a bird's-eye view map looking downobliquely from above; a bird's-eye view map generator for generating abird's-eye view map in accordance with road map data obtained from saidroad map data reader and said look down angle set by said angle setter;a car position detector having at least one of Global Positioning System(GPS) sensor, car speed sensor for detecting speed of the car and adirection sensor for detecting moving direction of the car, to detectpresent position of the car; and a display controller for displaying apresent position mark on a display apparatus in accordance with the setlook down angle on a position of the bird's-eye view map correspondingto car position detected by the car position detector, together withbird's-eye view map generated by the bird's-eye view map generator.
 2. Anavigation apparatus according to claim 1, further comprising: a mapgenerator for generating a plan view map in accordance with road mapdata obtained by said road map data reader, wherein said display controlapparatus coincides the shape of the present position mark to bedisplayed with the bird's-eye view map with the shape of the presentposition mark displayed on the plane view map in accordance with theposition of the car in displaying the plan view map, as the looking downangle approaches to 90 degrees in displaying the bird's-eye view map. 3.A navigation apparatus comprising: a road map data reader for obtainingroad map data; a bird's-eye view map generator for generating abird's-eye view map looking down obliquely from above, in accordancewith the road map data obtained by the road map data reader; a carposition detector having at least one of Global Positioning System (GPS)sensor, car speed sensor for detecting moving direction of the car, todetect position of the car moving on a road; a display controller fordisplaying a mark of shape on a display apparatus in accordance with aset look down angle on a position of the bird's-eye view mapcorresponding to car position detected by the car position detector,together with bird's-eye view map generated by the bird's-eye view mapgenerator; and a look down angle change detector for detecting change oflook down angle of the bird's-eye view map, wherein said bird's-eye viewmap generating means generates the bird's-eye view map in accordancewith the look down angle after the look down angle has changed, when achange of the look down angle is detected by the look down angle changedetector, and wherein said display controller displays a car mark on ashape of the display apparatus in accordance with the look down angleafter the look down angle has changed at the corresponding position ofthe car in accordance with the look down angle after the look down anglehas changed on the bird's-eye view map together with the bird's-eye viewmap in accordance with the look down angle after the look down angle haschanged, when a change of the look down angle is detected by the lookdown angle change detector.
 4. A navigation apparatus according to claim3, further comprising: a map generator for generating a plan view map inaccordance with road map data obtained by said road map data reader,wherein said display control apparatus coincides the shape of thepresent position mark to be displayed with the bird's-eye view map withthe shape of the present position mark displayed on the plane view mapin accordance with the position of the car in displaying the plan viewmap, as the looking down angle approaches to 90 degrees in displayingthe bird's-eye view map.
 5. A navigation apparatus comprising: a memoryfor storing map data for making a map of a predetermined region; anangle setter for setting a look down angle so as to generate abird's-eye view map looking down obliquely from above; a bird's-eye viewmap generator for generating a bird's-eye view map in accordance withthe map data obtained from said memory and the look down angle set bythe angle setter; a car position detector having at least one of GlobalPositioning System (GPS) sensor, car speed sensor for detecting speed ofthe car and a direction sensor for detecting moving direction of thecar, to detect present position of the car; and a display controller fordisplaying a present position mark on a display apparatus in accordancewith the set look down angle on a position of the bird's-eye view mapcorresponding to the car position detected by the car position detector,together with the bird's-eye view map generated by the bird's-eye viewmap generator.
 6. A navigation apparatus comprising: a memory forstoring map data for making a map of a predetermined region; abird's-eye view map generator for generating a bird's-eye view maplooking down obliquely from above, in accordance with the map dataobtained by the memory; a car position detector having at least one ofGlobal Positioning System (GPS) sensor, car speed sensor for detectingspeed of the car and a direction sensor for detecting moving directionof the car, to detect position of the car moving on a road; a displaycontroller for displaying a mark of a shape on a display apparatus inaccordance with the set look down angle on a position of the bird's-eyeview map corresponding to the car position detected by the car positiondetector, together with the bird's-eye view map generated by thebird's-eye view map generator; and a look down angle change detector fordetecting a change of look down angle of the bird's-eye view map,wherein said bird's-eye view map generating means generates thebird's-eye view map in accordance with the look down angle after thelook down angle has changed, when a change of the look down angle isdetected by the look down angle change detector, and wherein saiddisplay controller displays a car mark on a shape of the displayapparatus in accordance with the look down angle after the look downangle has changed at the corresponding position of the car in accordancewith the look down angle after the look down angle has changed on thebird's-eye view map, together with bird's-eye view map in accordancewith the look down angle after the look down angle has changed, when achange of the look down angle is detected by the look down angle changedetector.
 7. A navigation apparatus comprising: a road map data readerfor obtaining road map data; an angle setter for setting a look downangle so as to generate a bird's-eye view map looking down obliquelyfrom above; a perspective view map generator for generating aperspective view map by carrying out perspective transformation at anangle looking down obliquely from above, in accordance with the road mapdata obtained by the road map data reader; a car position detectorhaving at least one of Global Positioning System (GPS) sensor, car speedsensor for detecting speed of the car and a direction sensor fordetecting moving direction of the car, to detect a present position ofthe car; and a display controller for displaying a present position markon a display apparatus in accordance with the set look down angle on aposition of the bird's-eye view map corresponding to the car positiondetected by the car position detector, together with bird's-eye view mapgenerated by the bird's-eye view map generator.
 8. A navigationapparatus comprising: a road map data reader for obtaining road mapdata; a perspective view map generator for generating a perspective viewmap by carrying out perspective transformation at an angle looking downobliquely from above, in accordance with the road map data obtained bythe road map data reader; a car position detector having at least one ofGlobal Positioning System (GPS) sensor, car speed sensor for detectingmoving direction of the car, to detect position of the car moving on aroad; a display controller for displaying a mark of a shape on a displayapparatus in accordance with the set look down angle on a position ofthe perspective view map corresponding to car position detected by thecar position detector, together with the perspective view map generator;and a look down angle change detector for detecting a change of a lookdown angle of the perspective view map, wherein said perspective viewmap generating means generates the perspective view map in accordancewith the look down angle after the look down angle has changed, when achange of the look down angle is detected by the look down angle changedetector, and wherein said display controller displays a car mark on ashape of the display apparatus in accordance with the look down angleafter the look down angle has changed at the corresponding position ofthe car in accordance with the look down angle after the look down anglehas changed on the bird's-eye view map, together with perspective viewmap in accordance with the look down angle after the look down angle haschanged, when a change of the look down angle is detected by the lookdown angle change detector.